The structure and density of iron and iron-nickel alloys at Super-Earth core conditions

Laser-driven dynamic compression enables the study of material properties and equations of state at unprecedented extreme conditions. By carefully designing the laser pulse shape (i.e. laser power vs time), one can compress and heat the sample to a specific state, allowing the investigation of a wide range of pressures and temperatures. Specifically, “ramp”-compression can be used to reach extreme pressure conditions keeping the material in the solid state, by minimizing the entropy (and therefore temperature) increase associated with shock propagation.

The combination of laser-driven compression and x-ray diagnostics allows us to probe these extreme pressure-temperature conditions in-situ, providing a unique picture of the transformations taking place in high-energy-density matter with important applications for high pressure materials science, geophysics and planetary science. Structural probes, such as X-ray diffraction (XRD) have been developed at large laser facilities to investigate phase transitions and material properties at the nanosecond time scale.

In this talk, I will present results from X-ray diffraction and ramp-compression experiments carried out at the Omega Laser Facility, investigating structure and density of iron and iron-nickel alloys (80% and 90% iron content) up to 1 TPa and 0.6 TPa respectively, conditions expected in the interior of ~5 Earth Masses terrestrial extrasolar planets. The data reveal that the hexagonal-closed packed (hcp) structure is observed in both materials in the pressure range explored in our experiments. This observation will be discussed in the context of extrasolar planets interior structure.

This work was performed under the auspices of the US Department of Energy by Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344